1. Field of the Invention
In injectors for injecting fuel into the combustion chambers of internal combustion engines, high pressures occur in applications in injection systems with a high-pressure collection chamber (common rail), and these pressures have to be controlled in terms of the mechanical stresses on the injector. Care must also be take to assure an immediate response of the injection nozzle system to opening and closing movements, if precise metering of the fuel quantities to be injection is not to be impaired and the shaping of the course of injection is not to be incorrectly altered.
2. Description of the Prior Art
German patent DE 37 28 817 C2 relates to a fuel injection pump for an internal combustion engine. The control valve member used in the fuel injection pump comprises a valve stem, which forces a guide sleeve and slides in a conduit, and a valve head connected to the valve stem and oriented in the actuation direction. The sealing face of the valve head cooperates with the area of the control bore that forms the valve seat. The valve stem has a recess on its circumference whose axial length extends from the orifice of the fuel supply line to the beginning of the sealing face on the valve head that cooperates with the valve seat, and a face exposed to the pressure of the fuel supply line is embodied in the recess. This face is equal in size to a face of the valve head exposed to the pressure of the fuel supply line when the control valve is in the closed state. As a result, the valve is pressure-balanced in the closed state; in addition, a spring element that urges the control valve to its opening position is disposed in the guide sleeve of the control valve.
In known versions of injectors for injecting fuel that is at extremely high pressure into the combustion chambers of a direct-injection internal combustion engine, the high pressure prevailing in the high-pressure collection chamber (common rail) prevails permanently at the control valve. In such injectors, the poor closure of the nozzle at its seat face is disadvantageous. Poor closure of the nozzle at its seat face is due to the fact that the pressure has to be reduced over the distance between the control part and the nozzle seat in order to effect the closure of the nozzle needle. The longer the closing phase lasts, the greater can the incident leakage losses become, which has an extremely adverse effect on the efficiency of injectors.
With the version proposed by the invention, an injector for injecting fuel that is at high pressure can be designed such that a very high pressure prevails in the nozzle chamber of the injection nozzle when the nozzle needle opens. Furthermore, with the version proposed by the invention, fast needle closure can be assured.
The two control chambers embodied in the injector housing are acted upon, via suitable throttle elements, by the central fuel pressure prevailing from the high-pressure collection chamber. As a result, the high pressure prevailing in the high-pressure collection chamber also prevails at the branches, on the high-pressure inlet side, to the control chambers formed in the injector housing. These chambers are pressure-relieved simultaneously upon actuation of a control valve, and thus forced control of the opening motion of the nozzle needle is attainable by means of its vertical stroke in the injector housing. Embodying two control chambers in the injector housing makes it possible to adjust the nozzle system and the control part system independently of one another. By placing two inlet throttle elements upstream of the control chambers, both control chambers can be designed for optimal conditions for each. By direct action on a pressure shoulder face embodied in the nozzle chamber of the nozzle needle, the nozzle needle opens at its seat as soon as the nozzle chamber pressure exceeds the control chamber pressure. By simultaneous pressure relief of both control chambers provided in the injector housing, fast opening of the nozzle needle at its seat face can and hence a fast response of the injection nozzle can both be attained. A delay in the calculated injection onset and an attendant incorrect alteration of the injection pressure course from an overly slow pressure buildup in this inlet between the injection nozzle tip and the control part can thus be effectively counteracted.